Abstract: The present invention relates to an electric drive system for a bike comprising a portable electric friction drive device (1) and a bike bracket (13) configured to be mounted on a bike. A first drive device attachment point (3?) is located at a rear part of the friction drive device. A second drive device attachment point (4?) is located between the front part of the friction drive device and the rear part of the friction drive device so that the friction drive device is configured to rest against the second bracket attachment point (4). An inclination control arrangement (2) is configured to control the inclination of the imaginary line between the second drive device attachment point and a contact point (9?) of the drive wheel (9) by adjusting the tilt of the friction drive device over the second drive device attachment point. Further, the invention relates to a portable electric friction drive device.